1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method of semiconductor devices. In particular, the invention relates to a semiconductor device, and its manufacturing method, that includes a microprocessed silicon substrate upon which a Hall-effect element is mounted.
2. Description of the Related Art
Recently, micromachines, or micro electro mechanical system (MEMS), have been widely used as applications of LSI manufacturing technologies. To prepare a micromachine, a silicon substrate may be subjected to microprocessing technique, and required semiconductor elements are mounted on the processed silicon substrate. In manufacturing the micromachine, for instance, anisotropic etching including wet etching with an alkaline solution is employed to implement the microprocessing of the substrate. By the anisotropic etching, minute recesses can be accurately formed on the silicon substrate, into which semiconductor elements are disposed.
For example, JP-A-No. 2002-368304 discloses a resin-packaged semiconductor device in which a Hall-effect element is mounted on a lead frame. In this semiconductor device, the Hall-effect element is located on the opposite side across the lead frame compared with a conventional device, by which the distance between the magneto-sensitive surface of the Hall-effect element and an external magnet to be located outside the semiconductor device is shortened compared with the conventional device, without changing the thickness of the package. Shortening the mentioned distance leads to improved sensitivity of the Hall-effect element with respect to the change of magnetic flux.
When the Hall-effect element is mounted in the micromachine as semiconductor element, the recess has to be made deeper so as to shorten the distance between the Hall-effect element and the magnet, in order to improve the sensitivity of the Hall-effect element. This is because the Hall-effect element is mounted on the bottom surface of the recess, and hence when the micromachine is implemented on the surface of e.g. an external circuit board, the magnet is located close to the bottom surface, outside the micromachine. In the anisotropic etching process for forming the recess, a certain area of the bottom surface has to be secured to allow the Hall-effect element to be mounted thereon. The side faces of the recess are inclined with respect to the bottom surface, and therefore securing the certain area for the bottom surface leads to an increase in plane projection area of the recess, which in turn results in an increase in size of the micromachine as a whole.